In the Above Graph, If Bracket a Represents the Tidal

In the above graph, if Bracket A represents the tidal volume and Bracket B represents the vital capacity, respectively, of a young man, what does Bracket C represent?

A) anatomical dead space
B) air that is not used for gas exchange
C) air that helps keep the alveoli inflated (open) after forced exhalation
D) air from a previous breath that does not mix with newly-inhaled air of the next breath
E) air with a concentration of oxygen higher than that of air outside the body